1. Field of the Invention
This present invention relates to a sensor system, and more specifically to a feed detecting system for processing a feed detecting signal which is used in a scanner and a printer, etc.
2. The Related Art
Conventionally, a sheet-feeding apparatus is arranged in a scanner or a printer, for static electricity between papers or others reasons, two papers or more are fetched by the sheet-feeding apparatus in one time, the papers will block a paper passageway in the scanner or the printer, or a part of the paper will not be scanned or printed for being sheltered.
U.S. Pat. No. 7,172,195 has disclosed an image reading apparatus, the image reading apparatus comprises an ultrasonic wave sensor, the ultrasonic wave sensor includes a wave sending element and a wave receiving element having a same structure with the wave sending element. The wave receiving element and the wave sending element are arranged in the top and the bottom sides of the transport path of the image reading apparatus respectively. While a sheet passes through the image reading apparatus along the transport path, the wave sending element sends an ultrasonic signal to the sheet, the ultrasonic wave passes through the sheet, the ultrasonic wave is attenuated differently in case of one sheet and in case of two or more sheets. Then the ultrasonic wave is amplified, rectified and converted to digital signal, the digital signal is compared with a standard value stored in a control CPU, the standard value is indicated by the ultrasonic wave passing through a sheet. If the digital signal is greater than the standard value, no sheet passes through the transport path; if the digital signal is less than the standard value, two sheets or more pass through the transport path; if the digital signal equals with the standard value, one sheet passes through the transport path.
For converting the ultrasonic wave to a digital signal, an A/D converter is arranged in the image reading apparatus. In order to exactly detecting the ultrasonic wave, the A/D converter must be a high frequency A/D converter, the high frequency A/D converter is a high cost, so the cost of the image reading apparatus is improved.